The present invention relates to a mobile radio telephone system and, more particularly, to an improvement in terminal equipment of a vehicle radio telephone system.
A vehicle radio telephone system or similar mobile radio telephone system is extensively used today. This kind of telephone system includes terminal equipment each being controlled by a control section thereof which is implemented as a CPU, for example. Conventional terminal equipment for use in a vehicle radio telephone system has some problems left unsolved and some points which need improvements, as enumerated below.
(1) A vehicle radio telephone system has higher fees for calls than the other wire telephone systems because it uses electromagnetic waves which is the finite resource. In the light of this, it is a common practice to provide terminal equipment with a locking function for preventing unauthorized persons from using the equipment. The locking function is such that the equipment can be readily locked by any person allowed to use the equipment, but it cannot be unlocked unless a confidential unlocking code known only by the owner or the administrator is inputted to the equipment. The owner, administrator or similar authorized person, however, has to lock the equipment every time the person leaves the vehicle on which the equipment is mounted, so that the terminal may be prevented from being used by unauthorized persons when the vehicle is stolen. This, coupled with the fact that the authorized person has to lock the equipment every time he or she uses it, forces the authorized person to take extreme care in locking the equipment and thereby increases the mental burden.
(2) Some terminal equipment heretofore proposed for a vehicle radio telephone system have functions of limiting the area in which a call can be originated on the equipment, i.e., a function of limiting allowable calls only to local calls, a function of limiting them only to local and domestic calls, and a function of allowing all of the local, domestic and international calls. These three functions are selectively set up one at a time so as to prevent long-distance calls from being freely originated on the equipment. Of course, all of such limiting functions are set up only when a code number known exclusively by the authorized person is keyed in or otherwise inputted. For example, assume that a certain firm owns the terminal equipment, and that the communication area in which the persons expected to use the equipment, is a local area, and that these persons are employees who communicate for business transactions. Then, the administrator of the firm may limit the communicable area of the equipment to the local area for the purpose of inhibiting, for example, private calls meant for areas other than the expected business area such as long-distance calls and international calls which are expensive. This is successful in freeing the firm from wasteful expenditure and losses. A problem is, however, that every time the administrator allows an employee to use the equipment, the administrator has to set the communicable area again later. This is more pronounced when single terminal equipment is shared by a plurality of persons who are engaged in different kinds of work, e.g., when it is used in the morning by a person who needs only local calls, in the afternoon by another person who needs domestic calls, and at night by another person who needs international calls.
(3) In a vehicle radio communication system, a single identification (ID) code or telephone number is assigned to each terminal unit, and communications are held by using a single channel associated with the telephone number. Hence, a plurality of channels cannot be used unless the same number of terminal equipment as the channels are available. This prevents single terminal equipment from being used for different purposes on a time zone basis. Specifically, it is not practicable to connect single equipment to a certain channel in the daytime for a particular purpose and connect it to another channel in the nighttime for another purpose.
(4) The terminal equipment to which a single channel or telephone number is assigned as stated above is provided with a single memory. Hence, the content of data to be stored in the memory cannot be increased without resorting to extra telephone numbers which would complicate the operations of the equipment. Further, when the content of data to be stored in the memory differs from one time zone to another, all the contents have to be collectively stored in the single memory. It is difficult, therefore, to selectively read the stored contents out of the memory.
(5) Usually, the terminal equipment of a vehicle radio telephone system is not provided with a function of sensing light inside the vehicle cabin. Therefore, when the vehicle cabin is not illuminated in the evening or at night, the equipment is hard to operate because the space around the equipment is dark. To solve this drawback, it has been customary to continuously illuminate a keyboard provided on the equipment and a liquid crystal display a predetermined interval after the turn-on of the power source of the equipment or after a particular key on the keyboard has been pressed. It follows that the illumination is effected over the above-mentioned interval when the space around the equipment is light enough and does not need illumination, whereby the life of the power source or battery of the equipment is reduced.
(6) On reception of a call, the conventional terminal equipment generates an alert tone of predetermined volume at all times. Hence, when it is desired to change the set volume level in matching relation to the conditions in which the equipment is used, e.g., to select a medium volume level in the early morning, a high volume level in the daytime, and a low level volume in the nighttime, the volume level of the alert tone has to be switched over each time.